That would be ok with me, I would just do it as a separate commit. amd64 and arm64 seems like a reasonable starting point. How much bigger does the kernel binary get with those options configured?

As for enabling compressed user or kernel dumps by default, I'm not sure. It's probably the right configuration for a lot of systems. Note that compressing core dumps can consume a ton of CPU time; as a followup to this change we should look at adding a periodic sched_yield() or so somewhere in the write path. IMO this is especially important seeing as there's no way to abort a user core dump. I'd probably ask on -arch for opinions on compressing by default. One compromise might be to add installer support for configuring compressed dumps.